Tell me why sprints are better

I've been running for 3 months and am still overweight so am easing into it slowly. After reading up on proper sprinting technique I started to cut out my longer runs and concentrate on doing shorter, faster sessions. I was regularly doing 3 and 5 kilometer trail runs before. I wouldn't say they were chronic cardio though, as I would always do them fartlek style - jogging a bit but mostly brisk walking. This week I've done 3 sessions of about 15 mins, where I walk a bit to warm up, sprint like an enraged hippo for about 70 meters, then walk till I've gotten my breath back, sprint again, etc.

My thinking behind this is to do with muscle fibers. To become good at sprinting, you do sprints to turn your neutral fibers into fast-twitch ones. Too much long distance running will turn them into slow-twitch fibers. I would like to be fast and bulky rather than being like a typical slim marathoner.

I feel kind of smug for running faster than the skinny joggers on my run, then letting them catch me up again when I walk/stagger with a red face while recovering from each sprint. I get the feeling that I must be doing the right thing for my health and for becoming faster, because sprinting feels hard. Hard in a good way of course, but still, much harder than doing a long, slow run. (If you don't think sprinting is hard, try doing it while carrying an extra 90lbs of flab!)

It's still difficult to get my head around though. My body feels knackered after my run today but my mind is still going - 'Surely running less than 3 miles per week isn't enough? Surely less than 15 minutes isn't a real exercise session?' Please share any evidence, anecdotal or scientific, for why sprinting is actually an awesome lifestyle hack, and not just wishful thinking?

Quality over quantity. It's better to run all-out at maximum output than to jog slowly. More intense exercise is better than less intense. Also, it takes less time to do, so you can get back to doing other stuff quicker.

The answers you seek are all over the web, start by typing "poliquin" and "sprint" into google and reading what Poliquin has to say on the matter (he cites studies)

sprinting, from just about all angles, is better than jogging. Health markers, body composition (fat loss, muscle gain, etc) all improve with the addition of sprinting. This doesn't mean you should NEVER jog and ALWAYS sprint though, you shouldn't have to sprint more than 2x/week (and if you're going very intense, only once is fine) so you could always do a short jog a week as well.

Sprints are probably the only PB rule I no longer follow. Whether I did sprints outside, treadmill or did intervals on the stair-mill at high speed, they all would aggravate my piriformis syndrome. I can see how sprints are important and probably healthy, but if it hurts, then it's not worth it.

Hmm that's something for me to be mindful of. I have piriformis syndrome, although I've seen an improvement since going primal and taking up jogging, my only regular exercise before that was walking. I shall have to be very careful!

I will probably do less running sessions per week when I take up swimming once per week at some point soon. Hopefully that will be less aggravating for my butt!

from my personal experience - i used to only be able to run for a max of 2.5 mins at about 8km an hour. 2 weeks ago i started the fartlek training,
walking at 5.5km for 2 mins,
run at 13km for 1 min,
walk at 5km for 3 minutes,
run @13km 1 min etc.
2 weeks after doing this daily - i discovered at the weekend that i can now run for 5 mins without stopping at 8km! i was well impressed. I sweat just as much as if i had done 30 mins exercise and yet i have only spent 10 mins working out, it seems to be working for me and its great as its just a short period of time out of an already packed day!

i know everyone says you have to make time for things like this but the 10 mins fits in very well with my lifestyle at the moment. coupled with 2 days a week of 40-60 mins exercise, my fitness levels have seriously improved as a result.